Pentachlorophenol is industrially manufactured by the chlorination of phenol or the hydrolysis of hexachlorobenzene, but it always contains various kinds of phenolic acid substances and non-phenolic neutral substances as impurities.
Since among these impurities, however, there are found chlorodibenzodioxines and chlorodibenzofurans that are known to be strongly poisonous and their so-called precursors such as chlorodiphenyl ethers, chlorophenoxyphenols, and chlorodihydroxybiphenyls, when industrial pentachlorophenol is to be used as an agricultural chemical, it is required to remove the above described poisonous impurities.
In view of the above described situation the present inventor formerly developed a process of purification for industrial pentachlorophenol, which can advantageously remove the above described impurities contained therein (Japanese Patent Application No. 87982/1985).